Method of mounting vacuum tube electrodes



April-21, 1953 s. F. ESSIG 2,635,391

METHOD OF MOUNTING VACUUM TUBE ELECTRODES Filed July 2, 1951 EXHAUST PUMP l6 FIG. 7.

INVENTOR .5. E Essay;

ATTORNEY Patented Apr. 21, 1953 METHOD OF MOUNTING VACUUM TUBE ELECTRODES Sanford F. Essig, Fort Wayne, Ind., assignor to Farnsworth Research Corporation, Fort Wayne, Ind., a corporation of Indiana Application July 2, 1951, Serial No. 234,743

Claims. 1

This invention relates to methods of mounting vacuum tube electrodes and more particularly to methods of mounting electrode assemblies within glass envelopes for providing external connections through such glass envelopes.

In the manufacture of electron discharge tubes, it is always necessary to mount various electrodes or other elements within the envelope of the tube. In the conventional tubes of the triod type these electrodes are often mounted in a base plate of glass which may be later sealed to the glass envelope. However, in many types of tubes it is desirable to mount other electrodes within the tube having portions extending through the envelope at other parts than the base. One system has been proposed wherein an electrode lead may be sealed through a glass envelop by providing a glass bead on the end of thelead, which lead may be brought into contact externally of the envelope, the envelope then being heated to soften the glass and seal the rod and bead to the envelope. Pressure may be exerted against the end of this rod inside the envelope so as substantially to seal the rod flush with the inner side of the envelope. However, in this method there is generally still a thin film of the glass left on the end of the electrode lead which must be removed as by grinding before connections can be made to the electrodes within the envelope.

' It is an object of this invention to provide a method of mounting electrodes within an envelope with electrode leads extending outwardly through the envelope which will avoid the shortcomings of the methods previously used.

In accordance with a feature of this invention there is provided a method for sealing an elemerit within a glass envelope, preferably of tubular cross section,- which includes the steps of mounting the element inside the envelope with a portion or portions thereof substantially in contact with the interior of the envelope, heating the glass envelope locally in the region or regions of the'portions of the element in contact therewith to soften the glass so that it will partially collapse over these portions which are in contact and deforming the softened glass about these portions while the glass is still soft to retain the elements in place.

In accordance with a further feature of my invention the portions in contact with the envelope may be individual electrode leads which may be beaded at the end adjacent the envelope prior to the heating. Furthermore, a partial vacuum is preferably produced within the envelope to facilitate the collapse of the outer wall.

After the collapse a suitable tool, such as a prop erly shaped brush tool of graphite or preferably metal of such characteristics as the alloy Graph-Mo, may be used while the glass is still soft to clean ofi the glass from the portion of the lead extending externally of the envelope whereby in the complete assembly a rod for connection to external circuits is provided.

This method is particularly suitable for the mounting of the electron gun assemblies within the neck portion of cathode ray tubes and the like and is also further useful for the mounting of annular electrodes or electrode retaining elements in the walls of cylindrical tubes.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by referenc to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

Figs. 1, 2 and 3 are fragmentary views illustrating the application of the method steps in accordance with this invention for the mounting of an element with a lead extending through an envelope wall;

Figs. 4., 5 and 6 illustrate the various steps of an alternative type electrode structure mounted in accordance with the method of this invention; and

Fig. 7 is a cross sectional view of a tool for producing the final form of assembly as illustrated in Figs. 5 and 6.

Turning first to Fig. 1, the glass envelope wall shown at ll has mounted adjacent thereto an element 2 which may be an electrode to which is fastened a conductive rod 3. On the end of rod 3 may be provided a glass head 4'. The element 2 is positioned within the envelope so that the end of rod 3 carrying the glass bead 4 is substantially in contact with the inner surface of envelope Wall I. Heat may be applied locally to the area adjacent the point of contact of rod 3 and envelope l as, for example, by the burner shown diagrammatically at 5. Upon localized heating of the wall I the portion of the envelope adjacent rod 3 collapses as shown in Fig. 2 so that envelope Wall I is sealed to bead 4.

While the glass portion adjacent rod 3 is still soft a tool 6 is depressed over the end of rod 3 and causing the rod to pierce the glass wall. The operation also strips the glass film from the exposed portion of the rod. The end of rod 3 enters an opening I in tool 6 so that lead-out rod 3 extends externally of the envelope. Thus the electrode may be positioned precisely as it should be within the envelope, and the lead-out seal is made without disturbing the precise positioning of the electrode elements. To facilitate the collapse of the wall about the rod 3 the interior of the envelope may be partially evacuated so that the external air pressure will tend to push in the softened glass about the electrode rod.

It will be readily seen that this method is particularly good for mounting electrode assemblies of the type required in cathode ray electron guns as there may be several lead-out connections for various elements which are made through the neck of the tube. It is also clear that in such type of tubes the precise positioning of the gun with respect to the cathode ray screen is quite important and that by use of this method the precise positioning need not be disturbed during sealing. Even though it is desirable to have a partial vacuum during this sealing operation this may be accomplished by temporary enclosures. It is clear that suitable jigs may be used which can be removed later before the complete fabrication of the tube is completed and the final exhausting of the envelope made.

In certain types of tubes elements are mounted within the tube having output leads in the form of annular flanges extending through the glass envelope. This type of seal for example is common in tubes of the lighthouse type and is also applicable in many other types of high frequency tube structures. In Figs. 4, and 6 is shown a series of figures illustrating the manner in which the method of this invention is readily applicable to such tube construction.

Turning to Fig. 4 a portion of a cylindrical envelope is shown at 8 to which may be coupled an exhaust pump 9 through exhaust tubulation l0. Positioned within envelope 8 is provided an element H having a flange l2 which is substantially in contact with the cylindrical wall of envelope 8. Heat may be applied peripherally around envelope 8 as indicated by burners i3 and I4 so as to soften the glass in the vicinity of flange I2 is a ring around envelope 8. At the same time the pump 8 may be operated to reduce pressure within the envelope 8 so that the softened region in the wall will collapse inwardly around the edge of flange l2. While the glass is still soft .the portion of the envelope around the edge of flange l2 may be wiped with a tool I5 such as shown in Fig. '7. Tool [5 may be of graphite or some suitable metal and is provided with one or more slots or holes I6 and I1. The slots in practice vary progressively in width so that the final one fits the electrode and efiectively strips off the residual glass. If final form of envelope such as shown in Fig. 5 is desired, that is, with the flange substantially flush with the outer surface of the envelope 8 but shaped about the edge of the flange, the notch l6 may be used for wiping this periphery. On the other hand, if a final fonn of structure as shown in Fig. 6 is desired the narrow notch l 'l which is made substantially equal to the thickness of flange 12 is used for wiping this edge so that the 4 glass will be cleaned not only from the end of the flange l2 but from a portion of the sides of the flange external of envelope 8 as shown in Fig. 6.

It will be clear that the method as described above is applicable to many different type of electrode mountings and seals besides specifically illustrated.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A method of sealing an element within a glass envelope, comprising the steps of mounting the element in the envelope with portions thereof substantially in contact with the interior of said envelope, heating the glass of said envelope locally to softness in the vicinity of the points of said contact to partially collapse the envelope at said points, deforming said glass about said portions while soft to retain said element in place, and providing a partial vacuum within said envelope during said heating to facilitate collapse.

2. A method according to claim 1, wherein said deforming is such that said portions extend beyond the collapsed portion of said envelope, further comprising removing the glass from said portion extending beyond said collapsed wall while the glass is still in softened condition.

3. A method of sealing an electrode lead through the wall of a substantially tubular glass envelope comprising mounting said electrode lead within said tubular envelope with said lead substantially in contact with the wall of said envelope, partially evacuating said envelope and heating said wall to soften said glass in the vicinity of said lead, whereby the softened portion of said wall will collapse about said lead, and removing said softened glass from said lead external of said envelope to provide an uncovered output lead for said electrode.

4. The method according to claim 3, further comprising forming a glass bead on said lead prior to said mounting.

5. The method according to claim 3, wherein said electrode is formed with a flange lead substantially contacting the outer wall of said tubular glass envelope around its entire periphery, further comprising removing said softened glass from the entire peripheral edge of said flange external of said envelope wall.

SANFORD F. ESSIG.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,293,441 Housekeeper Feb. 4, 1919 2,340,459 Eitel Feb. 1, 1944 2,482,119 Mickley Sept. 20, 1949 

